Description

For the vEthernet, Ethernet, and management interfaces, you can configure the description parameter to provide a name for the interface. Using a unique name for each interface allows you to quickly identify the interface when you are looking at a listing of multiple interfaces.

By default, the description for vEthernet interfaces is automatically formatted to contain information about the connected device. The description for a virtual Network Interface Card (vNIC), for example, contains the VM name and network adapter number. You keep this default description or you can override it with a description of your choosing.

Speed and Duplex Modes

The speed and duplex modes are interrelated for each Ethernet and management interface. By default, each interface autonegotiates its speed and duplex modes with the other interface, but you can change these settings. If you change the settings, be sure to use the same speed and duplex mode settings on both interfaces or use autonegotiation for at least one of the interfaces.

Port MTU Size

The maximum transmission unit (MTU) size specifies the maximum frame size that an Ethernet port can process. For transmissions to occur between two ports, you must configure the same MTU size for both ports. A port drops any frames that exceed its MTU size.

By default, the MTU size for each port is 1500 bytes, which is the IEEE 802.3 standard for Ethernet frames. Larger MTU sizes are possible for more efficient processing of data with less overhead. The larger frames, called jumbo frames, can be up to 9000 bytes in size, which is also the fixed system jumbo MTU size in the Cisco Nexus 1000V.

Administrative Status

The administrative-status parameter determines whether an interface is up or down. When an interface is administratively down, it is disabled and unable to transmit data. When an interface is administratively up, it is enabled and able to transmit data.

Cisco Discovery Protocol

The Cisco Discovery Protocol (CDP) is a Layer 2 protocol that enables two devices that run CDP to learn about each other. You can use CDP to troubleshoot the network by displaying information about the neighboring devices that are linked through each interface. By default, CDP is enabled.

Port Channel

A port channel is an aggregation of multiple physical interfaces that comprise a logical interface. You can bundle up to eight individual interfaces into a port channel to provide increased bandwidth and redundancy. Port channeling also load balances traffic across these physical interfaces. The port channel stays operational if at least one physical interface within the port channel is operational.

Any configuration changes that you apply to the port channel are applied to each interface member of that port channel.

Guidelines and Limitations

Interface parameters have the following configuration guidelines and limitations:

You usually configure Ethernet port speed and duplex mode parameters to auto to allow negotiation of the speed and duplex modes between ports. If you decide to configure the port speed and duplex modes manually for these ports, consider the following:

If you set the Ethernet port speed to auto, the device automatically sets the duplex mode to auto.

If you enter the no speed, command the device automatically sets both the speed and duplex parameters to auto (the no speed command produces the same results as the speed auto command).

If you configure an Ethernet port speed to a value other than auto (for example, 10, 100, or 1000 Mbps), you must configure the connecting port to match. Do not configure the connecting port to negotiate the speed.

Note

The device cannot automatically negotiate the Ethernet port speed and duplex modes if the connecting port is configured to a value other than auto.

Note

Changing the Ethernet port speed and duplex mode configuration might shut down and reenable the interface.

To specify an interface in the CLI, use the following guidelines:

For an Ethernet port, use the ethernetslot/port command, where slot is the module slot number and port is the port number.

For a vEthernet port, use the vethernetnumber command, where number is a number from 1 to 1048575.

A space is not required between the interface type and the slot/port or interface number. For example, for the Ethernet slot 4, port 5 interface, you can specify either the ethernet 4/5 command or the ethernet4/5 command.

Configuring the Basic Interface Parameters

Specifying an Interface to Configure

You can specify an interface to configure.

Before You Begin

Log in to the CLI in EXEC mode.

Procedure

Command or Action

Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(config)# interfaceinterface

Enters interface configuration mode for the specified interface.

Step 3

switch( config-if)# show interfaceinterface

(Optional)

Displays the current configuration of interfaces.

The interface argument is defined as follows:

For an Ethernet port, use the ethernetslot/port command, where slot is the module slot number and port is the port number.

For the management interface, use the mgmt 0 or mgmt0 command.

For a vEthernet port, use the vethernetnumber command, where number is a number from 1 to 1048575.

Configuring the Interface Speed and Duplex Modes

You can configure the interface speed and duplex modes.

Before You Begin

Log in to the CLI in EXEC mode.

The interface speed and duplex modes are interrelated, so you should configure both at the same time. To see the speeds and duplex modes that you can configure together for Ethernet and management interfaces, see Speed and Duplex Modes.

Note

The interface speed that you specify can affect the duplex mode used for an interface, so you should set the speed before setting the duplex mode. If you set the speed for autonegotiation, the duplex mode is automatically set to be autonegotiated. If you specify a speed of 10 Mbps or 100 Mbps, the port is automatically configured to use half-duplex mode, but you can specify full-duplex mode instead. If you specify a speed of 1000 Mbps (1 Gbps) or faster, full duplex is automatically used.

Make sure that the remote port has a speed setting that supports your changes for the local port. If you want to set the local port to use a specific speed, you must set the remote port for the same speed or set the local port to automatically negotiate the speed.

For Ethernet ports on the 48-port, 10/100/1000 modules, sets the speed at 10 Mbps, 100 Mbps, or 1000 Mbps, or sets the port to auto negotiate its speed with the other 10/100/1000 port on the same link.

For Ethernet ports on the 32-port, 10-Gigabit Ethernet modules, sets the speed at 10,000 Mbps (10 Gbps) or sets the port to automatically negotiate its speed with the other 10-Gigabit Ethernet port on the link.

For management interfaces, sets the speed as 1000 Mbps or sets the port to autonegotiate its speed.

Step 3

switch(config-if)# duplex {full | half | auto}

Specifies the duplex mode as full, half, or autonegotiate.

Step 4

switch(config-if)# show interfaceinterface

(Optional)

(Optional) Displays the interface configuration.

Step 5

switch(config-if)# copy running-config startup-config

(Optional)

Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

This example shows how to set the interface description to Ethernet port 24 on module 3:

Enabling or Disabling CDP

You can enable or disable the Cisco Discovery Protocol (CDP) for Ethernet and management interfaces.

Before You Begin

Log in to the CLI in EXEC mode.

Make sure that CDP is enabled at both ends of the link.

Procedure

Command or Action

Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(config)# interfaceinterface

Specifies the interface that you are configuring. The interface argument is defined as follows:

For an Ethernet port, use the ethernetslot/port command, where slot is the module slot number and port is the port number.

For the management interface, use the mgmt 0 or mgmt0 command.

Step 3

switch(config-if)# [no] cdp enable

Enables or disables CDP for the interface in the running configuration. This parameter must be enabled for both interfaces on the same link. As soon as you disable CDP for one of two interfaces, CDP is disabled for the link.

Step 4

switch(config-if)# show interfaceinterface

(Optional)

Displays the CDP status for the interface in the running configuration. The interface argument is defined as follows:

For an Ethernet port, use the ethernetslot/port command, where slot is the module slot number and port is the port number.

For the management interface, use the mgmt 0 or mgmt0 command.

Step 5

switch(config-if)# copy running-config startup-config

(Optional)

Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.